1. Field of the Invention
The present invention relates to an apparatus for recovering a chrominance signal from a sequential color with memory (SECAM) composite video baseband signal (CVBS), and more particularly, to a frequency demodulator and method of recovering a SECAM chrominance signal to simplify a circuit configuration of a frequency demodulator and thereby perform a fixed-point calculation.
2. Description of Related Art
Generally, a composite video baseband signal (CVBS) is generated by synthesizing a video signal, a synchronizing signal, and the like, into a single signal. In this instance, the video signal contains encoding information which is needed to form video, and the synchronizing signal indicates display timing on a screen. Standards of the CVBS include National Television System Committee (NTSC), Phase Alternating Line (PAL), sequential color with memory (SECAM), and the like.
SECAM is a standard which was developed in France and was first used in broadcasting in the year 1967. Also, while NTSC and PAL utilize an amplitude modulation (AM) scheme for the color signal modulation technique, SECAM utilizes a frequency modulation (FM) scheme for a color signal modulation scheme.
SECAM constructs one scene with 625 scanning lines, transmits 25 scenes per second, and transmits 50 fields at the interlaced scanning of 2:1. Also, the bandwidth of DR and DB corresponding to chrominance signal components is limited to about 1.3 MHz. In order to prevent mutual interference between the chrominance signal components DR and DB, when transmitting a frequency-modulated chrominance signal component, SECAM alternatively transmits the chrominance signal components DR and DB every time a scanning line is changed.
An apparatus for recovering a chrominance signal from a CVBS, which is transmitted by a SECAM scheme, needs to calculate an arctangent in order to calculate a phase difference via a frequency demodulator. Schemes of approximating an arctangent function include various types of schemes, for example, a scheme of utilizing a Coordinate Rotation Digital Computer (CORDIC), a scheme of utilizing a lookup table, and the like.
However, in a conventional art, an apparatus for demodulating a SECAM CVBS approximates an arctangent function using a CORDIC or a lookup table to calculate a phase difference using a frequency demodulator. Accordingly, a process of calculating the phase difference is complex, which results in complicating a circuit configuration of the frequency demodulator.